What happened to wildlife when Chernobyl drove humans out? It thrived

People were evacuated after the Chernobyl accident, but what happened to the local wildlife? A new study shows that wildlife in the Chernobyl disaster zone is thriving, indicating that the presence of humans is more damaging to wildlife than is radiation poisoning

After a fire and explosion destroyed the Chernobyl Nuclear Power Plant in 1986, more than 100,000 people were permanently evacuated from the area to avoid radiation levels that were twenty times greater than the Hiroshima and Nagasaki bombings. But what happened to the local wildlife? According to a letter published today in the journal, Current Biology, scientists report that the Chernobyl disaster area is home to a rich and varied wildlife community, indicating that the mere presence of people is more damaging to wildlife than is radiation poisoning.

Chernobyl was a disaster for people, but for wildlife? Not so much

When the Chernobyl nuclear power plant melted down in 1986, more than 116,000 people were permanently relocated from a contaminated area comprising 4200 km2, an area that was later designated the Chernobyl exclusion zone.

But what happened to the local wildlife? Previous studies indicate that wildlife numbers initially dropped in the months after the accident (i.e.; doi:10.1098/rsbl.2008.0778). However, thirty years later, what effect is radiation contamination having on the abundance of Chernobyl’s large mammals?

An international team of researchers, headed by Tatiana Deryabina of the Polessye State Radioecological Reserve (PSRER), conducted surveys to find out. The PSRER is the Belarus sector of the Chernobyl exclusion zone. It covers 2,165 km2 (half of the total Chernobyl exclusion area) and has similar radiation levels to the Ukrainian sector. The findings for PSRER were compared to four nearby nature reserves that were uncontaminated by the Chernobyl accident: Berezinsky Biosphere Reserve, a state nature reserve covering 852 km2; Braslav Lakes National Park, which covers 645 km2; Belovezhskaya Puscha National Park, a UNESCO World Heritage site situated both in Poland (105 km2) and Belarus (1501 km2); and Narochansky National Park, which covers 874 km2. Of these, just two (Belovezhskaya Puscha and Narochansky National Park) allow limited wildlife hunting.

The team tested three fundamental hypotheses concerning the resilience of wildlife to the world’s worst nuclear accident:

Hypothesis 1: densities of mammals were suppressed due to the levels of radioactive contamination in the Chernobyl exclusion zone

Hypothesis 2: densities of large mammals were suppressed at PSRER compared with those in four uncontaminated nature reserves in Belarus

Hypothesis 3: densities of large mammals declined between 1 and 10 years after the accident

To test these hypotheses, trained staff conducted wildlife snow track censuses between 2008 and 2010 along 35 permanent track survey routes (total combined length of 315 km with an average track length of 9 km) (doi:10.1016/j.ecolind.2012.10.025). Specific PSRER habitat types (former agricultural lands, former villages, evergreen forest, and deciduous forest) and levels of radiocæsium contamination density were mapped using GIS along each of these routes.

Aerial surveys were conducted between 1987 and 1997 from February through early March when snow cover was present. The study area survey took place from a height of 100 metres at a speed of 70-100 km/h and extended to approximately 250 metres on each side of the helicopter.

As you can see, the empirical data show no evidence of long-term radiation damage to the large mammal populations at Chernobyl, and thus, the evidence does not support any of the three hypotheses being tested (Figure 1):

Figure 1. Animal abundances in the Chernobyl exclusion zone. (Top) Mean number of track counts per 10 km (in 2008–2010) for elk and wolf plotted against mean 137-Cs contamination density of each route. Analysis using linear mixed models including habitat variables found no evidence of correlation between mammal density and contamination density. (Bottom) Change in relative abundance of three species in the 10 years after the Chernobyl accident. Illustration: T.G. Deryabina et al (2015)/T.G. Deryabina et al/Current Biology 2015

In fact, increases in elk (moose) and wild boar populations in the Chernobyl exclusion zone occurred in the early 1990s, when these species’ populations were undergoing a rapid decline in former Soviet Union countries due to increased rural poverty and weakened wildlife management.

Further, the relative abundance of wolves living in and around the Chernobyl exclusion zone site is more than seven times greater than in the four nearby uncontaminated nature reserves.

Wolves were seven times more abundant in the Chernobyl exclusion zone site than in nearby uncontaminated nature reserves. Photograph: Valeriy Yurko/T.G. Deryabina et al/Current Biology 2015

“There have long been rumours that the Chernobyl site has abundant wildlife — including carnivores — so I welcome this piece”, said wildlife demographer Tim Coulson, a Professor of Zoology at the University of Oxford, who was not part of this study.

“Because it is contaminated land, it is not easy to study wildlife in detail, and any studies are going to have to rely on approaches like this taken here”, said Professor Coulson in email.

In fact, this study demonstrates that, regardless of potential radiation effects on individual animals, the Chernobyl exclusion zone supports a thriving and abundant mammal community despite nearly three decades of chronic radiation exposure.

“It’s very likely that wildlife numbers at Chernobyl are much higher than they were before the accident,” said co-author Jim Smith, a Professor of Environmental Science at the University of Portsmouth, in a press release.

Wild boar in the snow in the Chernobyl exclusion zone. Wild boar populations plummeted in 1993–1994 (Figure 1), due to a large increase in wolves as well as an outbreak of African swine fever. Photograph: Tatyana Deryabina/T.G. Deryabina et al/Current Biology 2015

Chernobyl’s wild boar populations grew especially fast -- until 1993-1994, when they suddenly crashed (Figure 1). This was due to a large increase in wolves, which are particularly fond of dining on wild boar, combined with an outbreak of African swine fever.

Humans are more damaging to wildlife and ecosystems than is radiation poisoning

“This study is a very positive move forward in conducting research concerning the potential health and environmental impacts of nuclear accidents”, said population biologist Timothy Mousseau, a Professor in the Biology Department at the University of South Carolina, who was not part of this study.

“I applaud the authors in their efforts to bring hard scientific data to bear on the question of impacts to wildlife in the stricken regions of Ukraine and Belarus. Much more research on this and related questions are desperately needed”, said Professor Mousseau in email.

“This doesn’t mean radiation is good for wildlife, just that the effects of human habitation, including hunting, farming, and forestry, are a lot worse,” said Professor Smith.

“This is an extremely sad indictment on how bad people are for wildlife”, agreed Professor Coulson. “Once [people] have left an area the wildlife appear to thrive — even if the habitat is laced with radiation.”

Although the detrimental effects of radiation on individual animals has been well documented, particularly on Chernobyl’s wildlife, its effects on populations isn’t so clear.

“This study does not address the issue of whether radiation has effects on reproduction, survival, longevity, or general health of the animals surveyed”, Professor Mousseau pointed out.

Nonetheless, this study indicates that populations of large mammals in the Chernobyl exclusion zone are doing at least as well as those in uncontaminated national parks in the vicinity. But sadly, this study clearly shows that putting a big fence around an area to keep people out is beneficial to wildlife, even if the negative effects of radiation contamination on wildlife -- increased mutation rates, cancers and other abnormalities -- may be masked by this advantage.

“Obviously I am not condoning nuclear accidents for the sake of wildlife! Far from it”, said Professor Coulson. “But hopefully some good can come from it. Hopefully we will realise that for wildlife and ecosystems to flourish, we must leave them be and stop interfering.”

In short, this paper suggests that not every nuclear wilderness is a bad thing.